I have a book with the front cover as an svg format. I have two issues with it. 1. it wont validate cause of this and two I have never used one before. I was wanting to know what are others take on it is?? It appears to allow the image to be stretched for the whole page. When I add an img tag to it I still have padding around the image. Suggestions??

Remove de DOCTYPE line. That DOCTYPE is for XHTML-only content, and you are including an <svg>, which belongs to a different type, that's why the W3C validator fails (it's not valid XHTML, as declared by its DOCTYPE)

Epubcheck accepts it as valid because (I believe) ePub explicitly allows documents including both XHTML and SVG content.

The DOCTYPE line is optional, but if it's present, it must be correct. The one you have is not, so it should be removed, and I think epubcheck should give it as an error too.